CPP with elongated pinned layer

ABSTRACT

CPP magnetic read head designs have been improved by increasing the length of the AFM layer relative to that of both the free and spacer layers. The length of the pinned layer is also increased, but by a lesser amount, an abutting conductive layer being inserted to fill the remaining space over the AFM layer. The extended pinned layer increases the probability of spin interaction while the added conducting layer serves to divert sensor current away from the bottom magnetic shield which now is no longer needed for use as a lead.

This is a divisional application of U.S. patent application Ser. No.10/991,583, filed on Nov. 18, 2004, now U.S. Pat. No. 7,382,589, whichis herein incorporated by reference in its entirety, and assigned to acommon assignee.

FIELD OF THE INVENTION

The invention relates to the general field of magnetic GMR-type readheads with particular reference to GMR enhancement in a CPP device.

BACKGROUND OF THE INVENTION

The principle governing the operation of most magnetic read heads is thechange of resistivity of certain materials in the presence of a magneticfield (magneto-resistance or MR). Magneto-resistance can besignificantly increased by means of a structure known as a spin valvewhere the resistance increase (known as Giant Magneto-Resistance or GMR)derives from the fact that electrons in a magnetized solid are subjectto significantly less scattering by the lattice when their ownmagnetization vectors (due to spin) are parallel (as opposed toanti-parallel) to the direction of magnetization of their environment.

The main elements of a spin valve can be seen in FIG. 1. They are lowershield/conductor layer 11 on which is (magnetically) free layer 12.Directly above the free layer is non-magnetic spacer layer 13 and aboveit is a (magnetically) pinned layer 14. Pinning of the latter iseffected by antiferromagnetic (AFM) layer 15. Note that the pinned layermay be a single magnetically soft material such as NiFe or it could be asynthetic antiferromagnet formed by sandwiching an antiferromagneticcoupling layer between two antiparallel ferromagnetic layers. Thetopmost layer is magnetic shield layer 16 which also serves as aconductive lead for the device.

In the device illustrated in FIG. 1, the direction of current flow isshown as arrow 17. In other words, the current runs perpendicular to theplane of the device which is therefore referred to as a CPP device. Itis also possible to arrange for the conductive leads to abut thevertical sidewalls of the GMR pedestal, in which case the structurebecomes a CIP (current in plane) device. As track width grow narrower,the trend has been to favor CPP devices.

The device illustrated in FIG. 2 is essentially the same as the one seenin FIG. 1 except that the order of the elements making up the spin valvehas been reversed. Both devices operate in the same way—When free layer12 is exposed to an external magnetic field, the direction of itsmagnetization is free to rotate according to the direction of theexternal field. After the external field is removed, the magnetizationof the free layer will be at a direction, which is dictated by theminimum energy state, determined by the crystalline and shapeanisotropy, current field, coupling field and demagnetization field.

If the direction of the pinned field is parallel to the free layer,electrons passing between the free and pinned layers suffer lessscattering. Thus, the resistance in this state is lower. If, however,the magnetization of the pinned layer is anti-parallel to that of thefree layer, electrons moving from one layer into the other will suffermore scattering so the resistance of the structure will increase. Thechange in resistance of a device of this type is typically 8-20%.

As magnetic recording densities get beyond 100 Gbpsi, the CPP GMR sensorbecomes the reader of choice. It has the advantage of bettersignal-to-noise ratio and, also, its signal amplitude does not scaledown with device dimensions which is a necessary quality as trackdensities get higher. However, the signal amplitude of a CPP head isgenerally too small to be practically useful, because of low dR/R. Thepresent invention discloses how this shortcoming can be overcome.

This change of resistance, dR, can be detected as a signal voltage whena current passes through. Note that the sensing current in CPP mode isflowing perpendicular to GMR stack. dR, which represents a signalamplitude, depends on the materials chosen for the free and pinnedlayers as well as their neighboring layers. It also depends on geometryof the device. The material is normally characterized by the bulk spinasymmetry coefficient and the interface spin asymmetry coefficient. ThedR contribution depends on how long electrons can interact in the bulk.Since the thickness of a CPP device is relatively small, being limitedby the shield-to-shield spacing, it cannot contribute much and thereforethe signal that can be detected is limited.

Current CPP GMR configuration suffers from an additional problem. Thetotal device resistance comprises both the GMR and parasiticresistances, with the latter dominating. The result is degradation ofdR/R to a very small value.

A routine search of the prior art was performed with the followingreferences of interest being found:

GMR structures are disclosed in U.S. Pat. No. 5,576,914 (Rottmayer etal) and in U.S. Pat. No. 6,084,752 (Sakakima et al). In U.S. Pat. No.5,668,688, Dykes et al describe a conductor on top of the pinning layerwhile Yuan et al. show conductor layers adjacent to each end of the GMRin U.S. Pat. Nos. 6,219,205 and 5,739,987.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to provide an improved CPP GMR magnetic read head.

Another object of at least one embodiment of the present invention hasbeen to Improve dR by increasing the length of spin interaction.

Still another object of at least one embodiment of the present inventionhas been to reduce parasitic resistance by largely bypassing the AFMlayer

A further object of at least one embodiment of the present invention hasbeen to reduce shield-to-shield spacing by eliminating a conductor layerin the gap.

These objects have been achieved by increasing the length of the AFMlayer relative to that of both the free and spacer layers. The length ofthe pinned layer is also increased, but by a lesser amount, an abuttingconductive layer being inserted to fill the remaining space over the AFMlayer. The extended pinned layer increases the probability of spininteraction while the added conducting layer serves to divert sensorcurrent away from the bottom magnetic shield which is now no longerneeded for use as a lead.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show prior art examples of CPP GMR read heads.

FIGS. 3 a and 3 b show a CPP read head modified according to theteachings of the present invention.

FIGS. 4 and 5 show two stages of the process of the invention.

FIG. 6 is an isometric view of the structure shown in FIG. 3 a.

FIG. 7 is an isometric view of the completed structure

FIG. 8 illustrates how longitudinal bias is provided to the structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention includes two novel features:

1. Elongating both the pinned and the pinning layers at the back side.The increased length is about 0.05 microns.

2. A conductor is added and abutted to the pinned and/or pinning layers.

The result of these features is that the bias current is forced to flowfrom the top conductor down through free layer and spacer and then toturn at the pinned layer, running out at the back side and entering theconducting lead. Thus only a portion of the bias current flows becauseof its high resistance.

Since the current flows in the elongated pinned layer, it has a longerinteraction distance and therefore, dR is increased.

Since the current bypasses the high resistance (parasitic) portion ofthe head circuit, total R is reduced, thereby increasing dR/R.

In some prior art, a highly conductive layer is inserted between themagnetic shield and the AFM layer in order to direct current flow.However, this increases the total GMR height, making a very smallshield-to-shield spacing impossible. The larger PW50 (pulse width at 50%amplitude) that is thereby induced will exclude it from very high lineardensity applications. In the present invention, the conductor is removedto the back side, enabling us to maintain a small shield-to-shieldspacing.

We will now describe a process for manufacturing the present invention.Said description will also make clear the structure of the presentinvention.

Referring now to FIG. 3 b, the process of the present invention beginswith the provision of a substrate (not shown) onto which is depositedbottom magnetic shield layer 11. Optionally, dielectric layer 41 isdeposited onto shield 11. This dielectric layer is typically of aluminaor silica and is between about 10 and 50 Angstroms thick. If it iselected to omit this layer, the structure will then be as seen in FIG. 3a.

Now follows the formation (on either dielectric layer 41 or bottomshield 11) of a CPP stack that is made up of free layer 12, spacer layer13, pinned layer 34 and pinning layer 35. As seen in FIG. 3 a or 3 b,the width of this stack is then made to be less than that of the bottomshield 11 by etching down to layer 11 (or 41 if used), there being acentrally located photoresist mask on layer 12 (not shown, but having awidth between about 3 and 10 microns).

Using a fresh photoresist mask that is narrower than the CPP stack(being between about 0.15 and 3 microns wide), the unprotected parts ofthe CPP stack are removed down as far as pinning layer 35. Then, as akey feature of the invention, layer 36 of conductive material isdeposited onto the exposed portions of pinning layer 35. Layer 36 istypically any good conductor such as Cu, Au, Al, or AlCu and it isbetween about 100 and 300 Angstroms thick. Following this thephotoresist mask is removed together with all conductive material thatwas deposited thereon, giving the structure the appearance illustratedin FIG. 4.

A third photoresist mask narrower than the previous mask (having a widthbetween about 0.05 and 0.15 microns) is then used to define the readtrack width, following which the unprotected parts of the CPP stack areremoved down to the level of the pinned layer. As can be seen in FIG. 5,a method, such as ion beam milling or etching, is used so that theremaining stack 81 (originally layers 12 and 13) is given slopingsidewalls. These are necessary for the opposing longitudinal bias layersto be effective, as will be seen a little later.

At this point in the process of the invention the structure has theappearance shown in isometric projection in FIG. 6. Proceeding with thestandard process, layer of dielectric material 83 is deposited on allexposed surfaces, including the above-mentioned sidewalls, Layer 83 isalumina or silica and is between about 50 and 300 Angstroms thick. Thisis followed by the deposition of longitudinal bias layer 82 ondielectric layer 83. as illustrated in FIG. 8. Finally, after removal ofthe photoresist, top magnetic shield layer 16 is deposited, giving thecompleted structure the appearance illustrated in FIG. 7, with a shieldto shield separation of 0.06 microns or less.

In summary then, starting at the bottom of FIG. 5, the structure of thepresent invention begins with lower magnetic shield layer 11.Optionally, in contact with all of layer 11 is insulating layer 41(which may be seen in FIG. 3 b). Layer 41 serves to minimize currentflow 37 away from the layers above it. AFM layer 35 lies on insulatinglayer 41 (if this option was used) and its outside ends do not extendout as far as 11 does, being between about 3 and 10 microns long.

Pinned layer 34 lies on AFM layer 35 and does not extend for the fulllength of 35 (being instead between about 0.15 and 0.3 microns long) theremaining space being taken up by conductive layer 36 that abuts theright edge (in the figure) of pinned layer 34. Conductive layer 36normally (but not necessarily) has the same thickness as 34 (betweenabout 100 and 2,000 Angstroms). Typical materials for layer 36 include(but are not limited to) Cu, Au, Al, and AlCu.

Non-magnetic spacer layer 13 lies on pinned layer 34. Its length is lessthan that of 34, being the conventional length normally associated withthis layer (between about 0.1 and 0.25 microns) as seen in the prior artexamples FIGS. 1 and 2. The remainder of the structure is also of aconventional nature—free layer 12 and top magnetic shield 16 which alsoserves as the top conductor lead. However, as a result of this design,the separation between the upper and lower magnetic shields has beenreduced to less than about 0.06 microns.

Once the process described earlier has been completed the structure isdivided into two equal halves whose (formerly common) ends are thenpolished to a high degree of planarity to become air bearing surfaces(ABS). This is best seen in FIGS. 6 and 7. Note that, for reasons ofimproved presentation, the longitudinal bias leads shown in FIG. 8 arenot shown in these figures even though they are part of the actualfinished product.

1. A process to manufacture a CPP magnetic read head, comprising:providing a bottom magnetic shield and depositing thereon a CPP stackthat comprises a free layer, having a top surface, said free layercontacting a spacer layer which contacts a pinned layer which is on apinning layer; forming a first photoresist mask on a central area ofsaid top surface and then removing unprotected parts of said CPP stackuntil said bottom magnetic shield layer is just exposed, followed byremoval of said first layer of photoresist; then forming a secondphotoresist mask, narrower than said first mask, on a central area ofsaid top surface and then removing unprotected parts of said CPP stackuntil opposing portions of said pinning layer are just exposed; withsaid second mask still in place, depositing a layer of a conductivematerial onto the exposed portions of the pinning layer; then removingsaid second mask, including all conductive material deposited thereon;then forming a third photoresist mask whose width defines a read trackhaving a width that is narrower than that of said second mask, on acentral area of said top surface, and then, using a method that resultsin sloping sidewalls, removing unprotected parts of said CPP stack untilopposing areas of said pinned layer are just exposed; with said thirdmask still on place, depositing a layer of dielectric material on allexposed surfaces, including said sidewalls, and then depositing alongitudinal bias layer on said dielectric layer; and then removing saidthird photoresist mask.
 2. The process recited in claim 1 wherein saidfirst photoresist mask has a width between about 3 and 10 microns. 3.The process recited in claim 1 wherein said second photoresist mask hasa width between about 0.15 and 0.3 microns.
 4. The process recited inclaim 1 wherein said third photoresist mask has a width between about0.1 and 0.25 microns.
 5. The process recited in claim 1 wherein saidconductive layer is selected from the group consisting of Cu, Au, Al,and AlCu and is between about 100 and 300 Angstroms thick.
 6. Theprocess recited in claim 1 wherein said dielectric layer is selectedfrom the group consisting of alumina and silica and is between about 10and 50 Angstroms thick.
 7. A process to manufacture a CPP magnetic readhead, comprising: providing a bottom magnetic shield and depositingthereon a first dielectric layer; forming on said first dielectric layera CPP stack that comprises a free layer, having a top surface, said freelayer contacting a spacer layer which contacts a pinned layer which ison a pinning layer; forming a first photoresist mask on a central areaof said top surface and then removing unprotected parts of said CPPstack until said first dielectric layer is just exposed, followed byremoval of said first layer of photoresist; then forming a secondphotoresist mask, narrower than said first mask, on a central area ofsaid top surface and then removing unprotected parts of said CPP stackuntil opposing portions of said pinning layer are just exposed; withsaid second mask still in place, depositing a layer of a conductivematerial onto the exposed portions of the pinning layer; then removingsaid second mask, including all conductive material deposited thereon;then forming a third photoresist mask whose width defines a read trackhaving a width that is narrower than that of said second mask, on acentral area of said top surface, and then, using a method that resultsin sloping sidewalls, removing unprotected parts of said CPP stack untilopposing areas of said pinned layer are just exposed; with said thirdmask still on place, depositing a layer of second dielectric material onall exposed surfaces, including said sidewalls, and then depositing alongitudinal bias layer on said second dielectric layer; and thenremoving said third photoresist mask.
 8. The process recited in claim 7wherein said first dielectric layer is selected from the groupconsisting of silica and alumina and is between about 10 and 50Angstroms thick.
 9. The process recited in claim 7 wherein said seconddielectric layer is selected from the group consisting of alumina andsilica and is between about 50 and 300 Angstroms thick.
 10. The processrecited in claim 7 wherein said bottom magnetic shield is between about1 and 3 microns thick and is separated from a top magnetic shield by nomore than about 0.06 microns.